Iam looking for function to do all maths

[skullJ]

Im working on univercity project and a part of my script is to calculate some maths.

All I need is to input varables into array and a mathematical action, and get the resolt as output.

 

For example:

<?php
$variables['l1'] = 100;
$variables['l2'] = 50;
$variables['x'] = 60;
$variables['y'] = 30;
$phrase = "c = (l1 ^ 2 - l2 ^ 2 + x ^ 2 + y ^ 2) / 2";
$result =  do_maths($phrase);
echo $result; // the result is 6000
php?>

 

I have some ideas and i can show you some code but all these drives me on deadend!

 

 

[Mchl]

1. There's no such thing as php?>

2. Look into eval

3. Look up RPN on Google

[JonnoTheDev]

I get a result of 72. Play about with it.

<?php
$variables['l1'] = 100;
$variables['l2'] = 50;
$variables['x']  = 60;
$variables['y']  = 30;
$result = ((($variables['l1'] ^ 2) - ($variables['l2'] ^ 2)) + (($variables['x'] ^ 2) + ($variables['y'] ^ 2))) / 2;
echo $result;
?>

[PFMaBiSmAd]

That's because ^ is a logical xor in php, not a pow() function.

[ignace]

3. Look up RPN on Google

 

How do you then handle 354 + 3? Or is it all separated by a space, but having an Assembler background I don't see how that could work as how would I know I had to read 1 byte, 2 bytes, 3 bytes?

[JonnoTheDev]

That's because ^ is a logical or in php, not a pow() function.

You can tell i'm crap at maths! Ah bitwise operator. Never used that before. PFMaBiSmAd, rewrite it buddy.

[Mchl]

@ignace: read until delimiter or operation symbol

[Daniel0]

3. Look up RPN on Google

 

How do you then handle 354 + 3? Or is it all separated by a space, but having an Assembler background I don't see how that could work as how would I know I had to read 1 byte, 2 bytes, 3 bytes?

 

It's stack based:

 

354 - adds 354 to the stack

3 - adds 3 to the stack, now it contains: 354 3

+ - pops an element from the stack and adds it. the stack now contains 357

 

If you traverse an abstract syntax tree in pre-order and just output the nodes to the screen instead of doing something with them, you'll get reverse polish notation.

[skullJ]

1. There's no such thing as php?>

2. Look into eval

3. Look up RPN on Google

 

so you propose to preg_replace the variables into numbers and then make maths with eval. Right?

[Ken2k7]

If you are using preg_replace, be careful with the regexp you're going to use. Make sure you are only replacing the variable. For example, if I have 2 variables: x and dxt, make sure you replace the x, but not also the x in dxt.

[skullJ]

If you are using preg_replace, be careful with the regexp you're going to use. Make sure you are only replacing the variable. For example, if I have 2 variables: x and dxt, make sure you replace the x, but not also the x in dxt.

 

that's exactly is that iam afraid of!!!!

 

Im already searching for patterns...and i hate them

[Mchl]

so you propose to preg_replace the variables into numbers and then make maths with eval. Right?

 

This too. But also you will have to replace 'x ^ y' with pow(x,y). That's why I hinted on converting the formula to RPN first. IIRC there are PEAR libriaries that you can use.

[skullJ]

What libraries? Can you explain this to me?

[Mchl]

http://pear.php.net/package/Math_RPN

[Daniel0]

Here is my take on a very simple one:

 

<?php
function math_rpn($expr)
{
$stack = array();

$getOps = function() use (&$stack) {
	if (count($stack) < 2) {
		throw new Exception('Invalid expression: not enough elements on stack');
	}

	$op2 = array_pop($stack);
	$op1 = array_pop($stack);
	return array($op1, $op2);
};

$tok = strtok($expr, ' ');
do {
	switch ($tok) {
		case '+':
			array_push($stack, array_sum($getOps()));
			break;
		case '-':
			list($op1, $op2) = $getOps();
			array_push($stack, $op1 - $op2);
			break;
		case '*':
			list($op1, $op2) = $getOps();
			array_push($stack, $op1 * $op2);
			break;
		case '/':
			list($op1, $op2) = $getOps();
			array_push($stack, $op1 / $op2);
			break;
		case '^':
			list($op1, $op2) = $getOps();
			array_push($stack, pow($op1, $op2));
			break;
		default:
			array_push($stack, $tok);
			break;
	}
} while ($tok = strtok(' '));

if (count($stack) !== 1) {
	throw new Exception('Invalid expression: end stack doesn\'t have exactly one element.');
}
return $stack[0];
}

echo math_rpn('1 2 + 5 * 2 /');

[skullJ]

RPN is working!

 

This is my first example with RPN:

 

<?php
include('RPN.php');

function do_maths($expr){
global $variables;

foreach($variables as $key => $value) {
$expr = str_replace($key, $value, $expr);
}

     $rpn = new Math_Rpn();
     $result = $rpn->calculate($expr,'deg',false);

return $result;
}

$variables['l1'] = 100;
$variables['l2'] = 50;
$variables['x'] = 60;
$variables['y'] = 30;
$phrase = "c = (l1 ^ 2 - l2 ^ 2 + x ^ 2 + y ^ 2) / 2";
$phrase = explode('=',$phrase);
$result =  do_maths($phrase[1]);

echo $result; // the result is 6000
?>

 

But i really dont have luck with patterns and im using str_replace.

Can anyone help me with pattern?